Role of mutant in seeding development

1. Use of mutants in
understanding seedling
development
Dr. Renu Jangid

2. Gene Expression During Seedling growth
• Development of the seedling covers a wide spectrum of activities ranging from
the sensing of an environmental or a hormonal stimulus to the control of growth
by cell division and cell elongation.
• Several investigators have identified mRNAs that accumulate preferentially in the
seedlings as they enter the autotrophic phase of growth.
• In soybeans, a subset of mRNAs appears in the emerging radicle, and another set
is abundant in the hypocotyl seedling axis at a later stage of germination.

3. • One of the mRNAs that accumulates in the hypocotyl seedling axis encodes a
proline- and hydroxyproline-rich protein that shows a modest sequence
homology to the well-known cell wall protein extension.
• Wheat seedlings enter the autotrophic phase of growth coincident with the
synthesis of a 28-kDa protein called germin. It is synthesized in the stem and
root and to a lesser extent in the leaves of wheat seedlings. The amino acid
sequence of germin favors its role in sugar uptake, cell wall synthesis, or
membrane repair in the growing seedling axis.

4. Embryogenesis Requires Specific Gene Expression
Analysis of Arabidopsis mutants that either fail to establish axial polarity or develop
abnormally during embryogenesis has led to the identification of genes whose
expression participates in tissue patterning during embryogenesis.
• The GNOM gene: Axial patterning
GNOM encodes a guanine nucleotide exchange factor
(GEF), which enables the directional transport of auxin
by establishing a polar distribution of PIN auxin efflux
carriers. Mutants, gnom embryos are spherical and lack
axial polarity entirely.

5. • We can conclude that GNOM gene expression is required for the establishment of
axial polarity.
The MONOPTEROS gene: It necessary for the
normal formation of basal region such as the root and
hypocotyl, encodes an auxin response transcription
factor (ARF). Mutations in the MONOPTEROS (MP)
gene result in seedlings that lack both a hypocotyl and
a root, although they do produce an apical region.

7. FACKEL (FK) gene: was originally interpreted to be
required for hypocotyl formation. Mutants exhibit
complex pattern formation defects that include
malformed cotyledons, short hypocotyl and root, and
often multiple shoot and root meristems. FK encodes a
sterol C-14 reductase, suggesting that sterols are critical
for pattern formation during embryogenesis.